Second driver ridiculously slow. Is this normal?

So I finally think I'm ready to do a 24h Le Mans. The invitational race with Ferrari 512. After first stint, running in first, I though of giving the second stint to the AI driver. He lost all my lead by being really slow. Then got stuck behind a slower class car and carried on following him at less than half throttle. I put on a movie and waited to see that happens... after 5 laps he was still there. Stuck behind a 911 being continuously lapped by my car class.
Is this normal? He's utterly useless. I looked for a setting or upskill but cannot find anything. As things stand using the AI driver is a guaranteed last place.

Yes, happenned to me in the milk man achivement. How is a long race, I let the control of my car to the IA at the mid of the race, but he was about 10 seconds per lap slower than me and/or the other AI cars. The AI brakes and reduces to 3th in the turns of the Indianapolis, so I have to retake the control of the car to finish the event. Don't know if it happens in some combos or ever, but after that experience, didn't tried anymore.

Yea, I won't try it again either. At Le Mans of all places... there's a chance to overtake a slower car almost everywhere. Pointless. Bad news is the race will take me a lot longer than I originally thought now that I have to do the whole thing myself. I don't understand why AI swap is even an option if he's so slow. Up until now I didn't have anything major to complain about in PC2.

This is disappointing to hear, because I'd hoped to mimic the experience of driver swaps and the AI would perhaps run laps similar to what I was putting in on the car.

He won't even be close to your times. And it doesn't depend on your opponent setting. Besides me running on 80% I can overtake a backmarker regardless of AI skill setting. My "team mate" can't perform a single overtake. He's peerless at losing places though...